You can use any name you like as long as it is not for illegal purposes. If she wants to add a surnamw she can, but if she is still at school they would probably not recognise it , but over time with use, by the time she is an adult she will have ewstablished the use of the name andshe would not need permission to use it. i suggest she does this and see how it works out. If her father's name is on her birtth certificate then he has the4 right to refuse permission for any legal name change , if he isn't because yoiu were unmarried at the time of her birth and he failed to attend the register ofice to register her bith, she does not need his permission for anything unless there isd a subsequent court order.